1. Technical Field
The present invention relates to a valve device for pressure control in a combustion engine with a crankcase to which crankcase gases are guided during operation of the engine. The valve device is adapted for detecting the current pressure in the crankcase, and for opening and closing a connection between the crankcase and a suction pipe of the engine, depending on the detected pressure.
The invention also relates to a method for pressure control in a combustion engine that comprises (includes, but is not limited to) feeding crankcase gases, during operation of the engine, from a crankcase that forms part of the engine. The current pressure in the crankcase is detected, and a connection between the crankcase and a suction pipe of the engine is opened and closed depending on the detected pressure.
2. Background
In the field of vehicles provided with a combustion engine, various methods are utilized for treating the gases that are fed out from the engine in connection with combustion occurring therein. In this case, such exhaust gas treatment takes place for various reasons such as demands regarding purification of harmful pollutants in the exhaust gases and requirements regarding the engine""s fuel economy and service life.
In this connection, it is previously known to utilize arrangements for ventilating crankcase gases out from the engine""s crankcase. The crankcase gases are generated during operation in the respective combustion chambers of the engine and include a comparatively high concentration of hydrocarbons that can be combusted. The crankcase gases are guided from the combustion chamber, between the respective cylinder foder and piston rings of the respective engine cylinder, and then further on to the engine""s crankcase.
For environmental reasons, it is normally not acceptable to discharge the crankcase gases into the atmosphere. For this reason, it previously known to feed the crankcase gases from the engine""s crankcase back to a suitable point in connection with the engine""s inlet side. By means of such closed crankcase ventilation, the gases can be sucked into the engine""s air intake for combustion in the engine. By means of this return of the crankcase gases back to the engine""s inlet side, the discharges of harmful pollutants from the engine is reduced.
One problem that arises in connection with previously known arrangements of the above-mentioned type is that the crankcase gases normally contain a certain amount of oil in the form of small oil particles. This is due to the fact that the crankcase gases enter the engine""s oil sump where a certain part of the lubricating oil is transformed into a liquid xe2x80x9cmistxe2x80x9d that has small drops of oil. If these oil particles are allowed to return to the engine""s inlet side, undesirable coatings can form, for example, in the engine""s combustion chambers and on the valves.
The above-mentioned problem particularly concerns engines provided with turbine combinations. For example, today""s diesel engines for commercial vehicles are often provided with systems for turbo charging in which an increased amount of air is compressed in a compressor, and then fed into the engine. Normally, such systems also include an intercooler for cooling the air after being fed through the compressor. If the crankcase gases are fed to the compressor, the oil particles in the crankcase gases may cause a coating in the compressor that can result in an impaired efficiency in the compressor. Furthermore, the oil particles may cause a coating in the intercooler, which results in an impaired efficiency in the intercooler. Still further, there is a risk of the oil drops being sucked into the engine.
In order to solve the above-mentioned problems by way of preventing oil particles from being carried along with the crankcase gases to the engine""s suction pipe, various types of separation devices are utilized that are provided between the crankcase and the engine""s inlet pipe. For example, so-called screen separators, baffle separators and fine separators are utilized for separating the oil particles from the crankcase gases in different manners.
Furthermore, it can be assumed that the pressure in the crankcase normally must be kept very close to the surrounding atmospheric pressure since a too high overpressure in the crankcase may result in oil leakage out of the engine. In a corresponding manner, an undesired underpressure may result in penetration of dirt, via the engine""s gaskets, and further into the engine. Thus, there is a demand for accurate control of the pressure in the crankcase to maintain it within a predetermined acceptable interval.
One objective of the present invention is to provide a valve device for efficient ventilation of crankcase gases in a combustion engine, namely by maintaining an internal pressure within a prescribed range of atmospheric pressure.
This object is achieved by means of a valve device of the type described above, and is characterized by the fact that it includes a first valve adapted for assuming a condition or configuration between a first, opened position and a second, closed position depending on the detected pressure in the crankcase. A second valve is also included and adapted for assuming a condition or configuration between a first, opened position and a second, closed position depending on the condition or configuration of the first valve.
The object is also achieved by means of a method that includes controlling a first valve between a first, opened position and a second, closed position depending on the detected pressure in the crankcase, and controlling a second valve between a first, opened position and a second, closed position depending on the condition of the first valve.
Several advantages are attained by means of the invention. Primarily, it can be noted that the pressure in the crankcase can be controlled within a comparatively narrow predefined interval. This control is provided by in a servo-like functional manner regarding the two valves.
Preferably, the first valve comprises a flexible diaphragm which, depending on the detected pressure in the crankcase, causes a valve element to open and close an opening which connects the first valve with the second valve. Furthermore, the second valve preferably comprises a flexible diaphragm that, depending on the condition or configuration (open versus closed) of the first valve, is adapted to open and close the connection. In this manner, it is provided that the first valve can be formed so that the valve element only makes small movements during the pressure control process. As a consequence, the diaphragm in the first valve can be made comparatively small, which thus corresponds to small diaphragm movements and an insubstantial undesired influence from disturbing factors, for example forces which act from the diaphragm itself. This creates conditions for an accurate control, at the same time as the valve device can be constructed in a compact manner.